Identification of high temperature precipitation reactions in 2024 Al-Cu-Mg alloy through ultrasonic parameters

► Three transitions are identified. ► The formation and growth of GPB zones at 350 K. ► Dissolution of GPB zones and S″ phase at 490 K. ► Formation of S′ and S phases at 555 K. ► Differentials of ultrasonic velocity are identified as an effective tool.